Papers by Author: Lothar Ley

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Authors: N. Sieber, Thomas Seyller, Lothar Ley, M. Polcik, D. James, J.D. Riley, R.C.G. Leckey
Authors: Kun Yuan Gao, Thomas Seyller, Konstantin V. Emtsev, Lothar Ley, Florin Ciobanu, Gerhard Pensl
Abstract: Atomic Layer Deposited Al2O3 films on hydrogen-terminated 6H-SiC(0001) were annealed in hydrogen atmosphere and characterized by admittance spectroscopy measurement and photoelectron spectroscopy (PES). The resultant density of interface trap (Dit) from admittance spectroscopy measurement is reduced near mid gap, but increases strongly towards the conduction band edge. Systematic PES measurements show that hydrogen annealing introduces Si4+ as a new component besides Si0 and Si+. Using different electron escape depths for photon electrons, depth profiling of Si in its different oxidation states was performed. The result indicates the formation of a top SiO2 layer and a rougher interfacial layer containing more Si+ and Si4+ which could be responsible for the strong increase of Dit just below the conduction band edge.
Authors: S. Rohmfeld, Martin Hundhausen, Lothar Ley
Authors: Roland Püsche, S. Rohmfeld, Martin Hundhausen, Lothar Ley
Authors: M. Hollering, N. Sieber, F. Maier, Jürgen Ristein, Lothar Ley, J.D. Riley, R.C.G. Leckey, F. Leisenberger, F. Netzer
Authors: M. Hollering, B. Mattern, F. Maier, Lothar Ley, A.P.J. Stampfl, J. Xue, J.D. Riley, R.C.G. Leckey
Authors: Roland Püsche, Martin Hundhausen, Lothar Ley, Kurt Semmelroth, Gerhard Pensl, Patrick Desperrier, Peter J. Wellmann, Eugene E. Haller, J.W. Ager, Ulrich Starke
Abstract: We study electronic Raman scattering of phosphorus and nitrogen doped silicon carbide (SiC) as a function of temperature in the range 7K < T < 300K. We observe a series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen and phosphorus donors on different lattice sites. These transitions are identified as valley orbit transitions of the 1s donor ground state. From the polarization dependence of the observed peaks, we find that all electronic Raman signals have E2-symmetry of C6v for the hexagonal polytypes (6H-SiC and 4H-SiC) and E-symmetry of C3v for 15R-SiC. We find a reduction of the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this reduction to the decreasing occupation of donor states.
Authors: Thomas Seyller, Konstantin V. Emtsev, Florian Speck, Kun Yuan Gao, Lothar Ley
Abstract: We have studied the electronic structure of the interface between 6H-SiC{0001} and graphite. On n-type and p-type 6H-SiC(0001) we observe Schottky barriers of ÁSi b,n = 0.3±0.1 eV and ÁSi b,p = 2.7±0.1 eV, respectively. The observed barrier is face specific: on n-type 6H- SiC(0001) we find ÁC b,n = 1.3±0.1 eV. The impact of these barriers on the electrical properties of metal/SiC contacts is discussed.
Authors: B. Herzog, S. Rohmfeld, Roland Püsche, Martin Hundhausen, Lothar Ley, Kurt Semmelroth, Gerhard Pensl
Authors: Jonas Röhrl, Martin Hundhausen, Konstantin V. Emtsev, Thomas Seyller, Lothar Ley
Abstract: We present a micro-Raman spectroscopy study on single- and few layer graphene (FLG) grown on the silicon terminated surface of 6H-silicon carbide (SiC). On the basis of the 2D-line (light scattering from two phonons close to the K-point in the Brillouin zone) we distinguish graphene mono- from bilayers or few layer graphene. Monolayers have a 2D-line consisting of only one component, whereas more than one component is observed for thicker graphene layers. Compared to the graphite the monolayer graphene lines are shifted to higher frequencies. We tentatively ascribe the corresponding phonon hardening to strain in the first graphene layer.
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